Well I have started myself with a C64 and got a lot of stuff still today.
Just as side note: if you pull the 6581 out of the SX-64 and scrap the comp. - you might end up in hell
So how to get some C64 Experience hmm, first setup the system with a bigger screen for normal use, like a 22" CRT TV and use splitted Chroma/Luma (so called S-Video).
For Sound use some Hifi-set.
Read the technical specification in the manual.
To start, leave the system in an unmodified state and try some programs from the Disk that came with the early C64s.
These are games like Jupiter Lander and Frogger f.e.
For the later experience get some speedloader first. For this, you can get some so called Multi Function Module, like Action Replay MK6 (4 or 5 will do also), Final Cartridge 3, Magic Formel 2.0, Nordic Power ....
If you can't get the Hardware get at least some software speedloader like Gigaload, GT 1, Heureka Sprint...
Now load games like: Paradroid, Parallax, Delta, Nebulus, Elite, Cybernoid II (long list of single file games here).
Also check the C64 Version of Maniac Mansion and ZakMcKracken.
Next step would be Katakis, Turrican I and II, Enforcer, Catalypse,X-Out,...
This is for games, now if you want to see some really incredible stuff try some of the latest scene demos:
Deus Ex Machinae, Natural Wonders, Sharp, Desert Dream and Second Reality Remake, Cycle, Dutch Breeze (go to www.c64.ch
Now recheck the technical specifications in the manual.